Trains are widely used to transport people and freight. Freight trains in particular may be relatively long and include several groups of locomotives (consists). For example, a freight train may be a mile long or more. Coordination is required for operating the locomotives to ensure proper traction and braking, for example.
U.S. Pat. Nos. 4,582,280 and 4,553,723 to Nichols et al. are seminal patents directed to a radio communication based train control system. The radio communication system is for a lead unit and a plurality of remote units. The system includes a protocol for establishing a communication link between the lead unit and the one or more remote units. The protocol prevents any of the units in the system from processing messages or commands from other units in other train systems or processing messages or commands originating from units with the train system but which are addressed to other units. A communications channel contention feature is provided for minimizing the probability of multiple units within the system from transmitting on the common communications channel at the same time. In addition, the system insures that the highest priority communications are transmitted first in time. The control system provides for the coordinated control of the air braking functions in the train.
Another application of computer based control systems relates to so-called "distributed power" (DP) functions. Such distributed power functions typically control locomotive tractive effort and dynamic braking as well as air brakes. In particular, GE HARRIS Railway Electronics, L.L.C. offers a radio based control system under the designation LOCOTROL.RTM. which provides coordinated distributed power and air brake control of the remote locomotives from the lead locomotive. The system controls tractive effort and braking effort for up to four consists for all types of freight over all types of terrain. Each equipped unit can be operated as a lead or a remote unit.
In certain applications it may be desirable to at least temporarily operate a train comprising two or more train segments, with each segment including at least one locomotive and plurality of railcars. For example, such train segments can be joined at an initial marshaling point and operated together for a portion of a journey. At another point, the individual train segments are disassembled and each train segment proceeds to its intended destination.
A typical train requires a continuous brake pipe connecting all locomotives and cars along the train. For the above described segmented train, the brake pipe in the past would typically be connected between the last car of a preceding segment with the next locomotive of the following train segment. Connecting the brake pipe and later disconnecting the brake pipe leads to considerable effort and manpower. Both assembly and later disassembly of the train segments are unnecessarily complicated by the traditional need for brake pipe continuity.
In the setting of a helper locomotive used to temporarily assist a train up an incline, for example, U.S. Pat. No. 5,383,717 to Fernandez et al. discloses that the helper locomotive may be equipped with a head-of-train (HOT) unit, and the car just prior to helper locomotive is equipped with an end-of-train (EOT) unit. The lead locomotive at the front of the train is also equipped with a HOT unit. The brake pipe is stopped at the last car so that the brake pipe of the helper locomotive is separate from the rest of the train. Accordingly, the helper unit can more readily connect and disconnect from the train. The EOT unit communicates to the HOT unit of the helper locomotive and to the HOT of the lead locomotive. The EOT unit allows the helper locomotive to operates its brakes based upon mirroring the brake pipe pressure seen by the EOT unit.
Unfortunately, radio communication between the EOT unit and the HOT unit of the lead locomotive can be disrupted, as when the train passes a curve or passes through a tunnel, for example. Other conditions may also cause less efficient operation of the brakes between the train and the helper locomotive. In addition, there is no coordination between the motive power of the locomotives of the train and the helper locomotive. Accordingly, potentially damaging forces may be generated between portions of the train.